The present invention relates to methods for use in the identification of molecules which bind to a target component of a biochemical system or modulate the activity of a target.
Over the past decade, high-throughput screening (HTS) of compound libraries has become a cornerstone technology of pharmaceutical research. Investment into HTS is substantial. A current estimate is that biological screening and preclinical pharmacological testing alone account for ˜14% of the total research and development (R&D) expenditures of the pharmaceutical industry (Handen, Summer 2002). HTS has seen significant improvements in recent years, driven by a need to reduce operating costs and increase the number of compounds and targets that can be screened. Conventional 96-well plates have now largely been replaced by 384-well, 1536-well and even 3456-well formats. This, combined with commercially available plate-handling robotics allows the screening of 100,000 assays per day, or more, and significantly cuts costs per assay due to the miniaturisation of the assays.
HTS is complemented by several other developments. Combinatorial chemistry is a potent technology for creating large numbers of structurally related compounds for HTS. Currently, combinatorial synthesis mostly involves spatially resolved parallel synthesis. The number of compounds that can be synthesised is limited to hundreds or thousands but the compounds can be synthesised on a scale of milligrams or tens of milligrams, enabling full characterisation and even purification. Larger libraries can be synthesised using split synthesis on beads to generate one-bead-one compound libraries. This method is much less widely adopted due to a series of limitations including: the need for solid phase synthesis; difficulties characterising the final products (due to the shear numbers and small scale); the small amounts of compound on a bead being only sufficient for one or a few assays; the difficulty in identifying the structure of a hit compound, which often relies on tagging or encoding methods and complicates both synthesis and analysis. Despite this split synthesis and single bead analysis still has promise. Recently there have been significant developments in miniaturised screening and single bead analysis. For example, printing techniques allow protein-binding assays to be performed on a slide containing 10,800 compound spots, each of 1 nl volume (Hergenrother et al., 2000). Combichem has so far, however, generated only a limited number of lead compounds. As of April 2000, only 10 compounds with a combinatorial chemistry history had entered clinical development and all but three of these are (oligo)nucleotides or peptides (Adang and Hermkens, 2001). Indeed, despite enormous investments in both HTS and combinatorial chemistry during the past decade the number of new drugs introduced per year has remained constant at best.
Dynamic combinatorial chemistry (DCC) can also be used to create dynamic combinatorial libraries (DCLs) from a set of reversibly interchanging components, however the sizes of libraries created and screened to date are still fairly limited (≦40,000) (Ramstrom and Lehn, 2002).
Virtual screening (VS) (Lyne, 2002), in which large compound bases are searched using computational approaches to identify a subset of candidate molecules for testing may also be very useful when integrated with HTS. However, there are to date few studies that directly compare the performance of VS and HTS, and further validation is required.
Microfluidic technology has been applied to high throughput screening methods. For example, U.S. Pat. No. 6,508,988 describes combinatorial synthesis systems which rely on microfluidic flow to control the flow of reagents in a multichannel system. U.S. Pat. No. 5,942,056, and continuations thereof, describes a microfluidic test system for performing high throughput screening assays, wherein test compounds can be flowed though a plurality of channels to perform multiple reactions contemporaneously.
Despite all these developments, current screening throughput is still far from adequate. Recent estimates of the number of individual genes in the human genome (˜30,000) and the number of unique chemical structures theoretically attainable using existing chemistries suggests that an enormous number of assays would be required to completely map the structure-activity space for all potential therapeutic targets (Burbaum, 1998).
Hence, the provision of a method which permits screening vast numbers (≧109) of compounds quickly, or smaller numbers of compounds under a range of conditions (different compound concentrations, different targets etc.) using reaction volumes of only a few femtoliters, and at very low cost would be of enormous utility in the generation of novel drug leads.
Tawfik and Griffiths (1998), and International patent application PCT/GB98/01889, describe a system for in vitro evolution using compartmentalisation in microcapsules to link genotype and phenotype at the molecular level. In Tawfik and Griffiths (1998), and in several embodiments of International patent application PCT/GB98/01889, the desired activity of a gene product results in a modification of the genetic element which encoded it (and is present in the same microcapsule). The modified genetic element can then be selected in a subsequent step.
The present invention is also based on compartmentalisation in microcapsules, in this case compartmentalisation of compounds from a compound library. The microcapsules are droplets of liquid made and manipulated using systems and methods for the control of fluidic species and, in particular, by systems and methods for the electronic control of fluidic species.
The manipulation of fluids to form fluid streams of desired configuration, discontinuous fluid streams, droplets, particles, dispersions, etc., for purposes of fluid delivery, product manufacture, analysis, and the like, is a relatively well-studied art. For example, highly monodisperse gas bubbles, less than 100 microns in diameter, have been produced using a technique referred to as capillary flow focusing. In this technique, gas is forced out of a capillary tube into a bath of liquid, the tube is positioned above a small orifice, and the contraction flow of the external liquid through this orifice focuses the gas into a thin jet which subsequently breaks into equal-sized bubbles via a capillary instability. In a related technique, a similar arrangement was used to produce liquid droplets in air.
An article entitled “Generation of Steady Liquid Microthreads and Micron-Sized Monodisperse Sprays and Gas Streams,” Phys. Rev. Lett., 80:2, Jan. 12, 1998, 285-288 (Ganan-Calvo) describes formation of a microscopic liquid thread by a laminar accelerating gas stream, giving rise to a fine spray.
An articled entitled “Dynamic Pattern Formation in a Vesicle-Generating Microfluidic Device,” Phys. Rev. Lett., 86:18, Apr. 30, 2001 (Thorsen, et al.) describes formation of a discontinuous water phase in a continuous oil phase via microfluidic cross-flow, specifically, by introducing water, at a “T” junction between two microfluidic channels, into flowing oil.
U.S. Pat. No. 6,120,666, issued Sep. 19, 2000, describes a micofabricated device having a fluid focusing chamber for spatially confining first and second sample fluid streams for analyzing microscopic particles in a fluid medium, for example in biological fluid analysis.
U.S. Pat. No. 6,116,516, issued Sep. 12, 2000, describes formation of a capillary microjet, and formation of a monodisperse aerosol via disassociation of the microjet.
U.S. Pat. No. 6,187,214, issued Feb. 13, 2001, describes atomized particles in a size range of from about 1 to about 5 microns, produced by the interaction of two immiscible fluids.
U.S. Pat. No. 6,248,378, issued Jun. 19, 2001, describes production of particles for introduction into food using a microjet and a monodisperse aerosol formed when the microjet dissociates.
Microfluidic systems have been described in a variety of contexts, typically in the context of miniaturized laboratory (e.g., clinical) analysis. Other uses have been described as well. For example, International Patent Publication No. WO 01/89789, published Nov. 29, 2001 by Anderson, et al., describes multi-level microfluidic systems that can be used to provide patterns of materials, such as biological materials and cells, on surfaces. Other publications describe microfluidic systems including valves, switches, and other components.
While significant advances have been made in dynamics at the macro or microfluidic scale, improved techniques and the results of these techniques are needed.